Protesters force St Louis mall to close

US protesters forced a crowded St Louis mall to close for around two hours, demanding a boycott to post-Thanksgiving shopping and justice for an unarmed black teenager killed by police.

Scores of demonstrators, including young children, shouted "No justice, no peace," and "Stop shopping and join the movement" at the St Louis Galleria Mall on Friday.

Around 100 people lay on the floor for four and a half minutes to symbolise the more than four hours that 18-year-old Michael Brown lay in the road after being shot dead by a white police officer in the St Louis suburb of Ferguson.

In New York, police made "several" arrests at a protest in front of Macy's flagship store in Herald Square, a spokesman said, without explaining why the demonstrators had been detained.

About 200 people gathered in support of the boycott of Black Friday, which comes the day after America's Thanksgiving holiday and sees stores offering steep discounts, leading to often-frenzied consumer spending.

In the San Francisco Bay area, protesters severely disrupted the BART mass transit system for more than two hours by blocking off a train station in Oakland, officials said.

The protesters chained themselves together at the West Oakland station, forcing trains to be stopped into and out of San Francisco, briefly stranding crowds including many heading to malls seeking Black Friday bargains.